The bulk of revenue earned by mobile communications is generated by voice traffic. A large share of that revenue is generated by roaming charges, which are incurred when a mobile phone cannot access the network to which it is registered and must access a different network. Mobile operators are assessed these roaming charges, such as Inter Operator Tariffs and Inter Exchange Carrier fees, which are ultimately passed on to the consumer.
To reduce these fees, mobile phone users take a variety of steps, such as using their mobile phones outside their registered network coverage area less often or changing Subscriber Identity Module (SIM) cards. When any of these steps are taken, the revenue generated by mobile operators is reduced and users are inconvenienced.
These drawbacks are also found with mobile telephones and other devices configured for Fixed Mobile Convergence (FMC). Such devices are able to access both fixed telephone networks, using wireless local area networks (WLAN), and mobile phone networks, using cellular networks, such as GSM or CDMA. These devices are not, however, capable of seamless roaming from one network into another for both voice and Short Message Service (SMS) messaging. Furthermore, there are no systems capable of authenticating, authorizing, and billing these devices as they roam using voice and SMS messages. Because users are similarly inconvenienced, unable to roam while exchanging voice and SMS messages, mobile operators suffer accordingly.